1. Field of the Invention
This invention relates to a composite beam, such as those used as crossarms for utility poles, having improved characteristics for transferring force more effectively over the beam to prevent structural weakening and failure.
2. Description of the Prior Art
Composite beams used as crossarms for utility poles have been proposed over the past few years for replacing wooden crossarms. These crossarms are usually formed of resin impregnated fiberglass materials. The composite crossarms are light, flexible, non-conductive and resistant to deterioration. Although an improvement over the wooden crossarms, composite crossarms have some disadvantages.
Composite fiberglass beams are typically formed as an outer casing or shell of resin impregnated fiberglass having a rectangular cross section. The outer casing may or may not be filled with a light weight filler material. Because certain areas of the cross arm encounter higher amounts of stress, these areas are typically reinforced more than others. Bolts used for mounting and stationing the crossarm are usually fastened to the crossarm by passing the bolts through the crossarm through holes located in opposite walls of the outer casing. Stress applied from the bolts often is concentrated around the corners of the casing where the opposite walls are joined. Even with reinforcement in these areas, the relative thinness of the walls at the corners and the high shear stresses that are encountered can result in failure under extreme loading. This is particularly a problem with dead end poles, which are subjected to much force.
What is needed is a composite beam construction that can withstand large amounts of force, such as applied by bolts, by spreading the force more uniformly over the beam to thus prevent failure during extreme loading.